Tide computation apparatus and method of using the same

ABSTRACT

Apparatus for computing the times of tides for a given date includes a base board having a first scale in the form of a spiral with index marks signifying the days of the year. A second circular scale signifying the hours of the day surrounds the first scale, and a third circular scale signifying the phases of the moon surrounds the second scale. A transparent cover plate or disc, which is provided with index marks for high and low tide, is mounted on the base board for rotation over the first scale about an axis concentric with the spiral and the circular scales. The surface of the disc is roughened so that it may be readily marked by pencil. A marker arm is mounted for rotation on the axis over the cover disc and has a straight edge which extends radially from the axis. A method is described involving the employment of tide tables and astronomical daily calendars of moon phases for scribing a &#39;&#39;&#39;&#39;home port date line&#39;&#39;&#39;&#39; and a &#39;&#39;&#39;&#39;moon line&#39;&#39;&#39;&#39; on the cover disc. When the &#39;&#39;&#39;&#39;home port date line&#39;&#39;&#39;&#39; is set over a given date on the first scale, index marks on the cover disc point to the times of tides on the given date and the &#39;&#39;&#39;&#39;moon line&#39;&#39;&#39;&#39; points to the phase of the moon for the given date.

United States Patent 1 Spilhaus [111 3,745,313 1 July 10, 1973 TIDE COMPUTATION APPARATUS AND METHOD OF USING THE SAME [75] Inventor: Atlielstan F. Spilhaus, Washington,

[73] Assignee: Nautilus Press, Inc., Washington,

[22] Filed: June 13, 1972 [21] Appl. No.: 262,301

Primary Examiner-Stephen J. Tomsky Attorney-Raphael Semmes [5 7 ABSTRACT Apparatus for computing the timesof tides for a given date includes a base board having a first scale in the form of a spiral with index marks signifying the days of the year. A second circular scale signifying the hours of the day surrounds the first scale, and a third circular scale signifying the phases of the moon surrounds the second scale. A transparent cover plate or disc, which is provided with index marks for high and low tide, is mounted on the base board for rotation over the first scale about an axis concentric with the spiral and the circular scales. The surface of the disc is roughened so that it may be readily marked by pencil. A marker arm is mounted for rotation on the axis over the cover disc and has a straight edge which extends radially from the axis. A method is described involving the employment of tide tables and astronomical daily calendars of moon phases for scribing a home port date line" and a moon line on the cover disc. When the home port date line is set over a given date on the first scale, index marks on the cover disc point to the times of tides on the given date and the moon line points to the phase of the moon for the given date.

13 Claims, 3 Drawing Figures HOME PORT DATE LINE MdoN LlNE IQO SUNSET HOME PORT DATE LINE 3 Sheets-Sheet 1 FIG. 1

SPRI

MdoN LINE Patented July 10, 1973 3,745,313

3 Sheets-Sheet 2 FIG. 2 4

I Patent ed July 10, 1973 3,745,313

3 Sheets-Sheet 5 TIDE COMPUTATION APPARATUS AND METHOD OF USING THE SAME BACKGROUND OF THE INVENTION This invention relates to computing apparatus and, more particularly, to apparatus for computing the time of tides for a given port on a given date and the phases of the moon on the given date. The invention also relates to a method of using the tide computation apparatus.

It has been customary in the past, when it was desired to determine the time of tides for a given home port, to employ tide tables which are prepared for most prominent ports. These tables customarily list the ports and dates with the times of the various tides on those dates. While accurate tide information may be obtained in this way, the use of the tables each time tide time information is required is tedious and inconvenient. In like manner, it has been customary, when it has been desired to determine the phases of the moon for a given date, to consult daily astronomical calendars which are found in prominent newspapers or world almanacs and the like. I-Iere, also, it has been inconvenient to consult an astronomical calendar each time this information is required.

SUMMARY OF THE INVENTION It is accordingly a principal object of the present invention to provide tide computation apparatus for facilitating quick and accurate determination of the time of tides at a given home port for a given date. An ancillary object is the provision of apparatus of this character which also provides information as to the phases of the moon for the given date. It is a further object of the invention to provide a method for using such apparatus in providing the desired information.

Briefly, the invention contemplates the provision of a special tide rule or tide computation apparatus. This apparatus comprises a base board having a first scale provided with a plurality of index marks signifying the days of the year and a second scale having a plurality of index marks signifying the hours of the day. The first scale has a plurality of successive sections each extending along the second scale. In a preferred embodiment,

' the first scale is provided in the form of a spiral with the successive convolutions of the spiral forming the successive sections of the scale. In this embodiment, the second scale is circular and is, in turn, surrounded by a third circular scale depicting the phases of the moon. A transparent cover plate overlies the base board and scales, the cover plate having indicia thereon signifying the stages of the tides. An arm is mounted for rotation over the cover plate and has a straight edge for facilitating the scribing oflines on the cover plate. The number of convolutions of the spiral scale is determined by dividing the number of days in a lunar month into the number of days in a year; this computation also determines the angle between the index marks. In order to avoid the necessity to reset the apparatus in leap years, the outermost date on the spiral first scale is Mar. 1, and the innermost date of the spiral is Feb. 29. In order to accommodate for the fifty minute change in the time of a tide from day to day, a vernier technique is used involving the shifting of index marks on the cover plate for successive high and low tides a fractional portion of 50 minutes.

The method according to the present invention involves the provision of the computation apparatus, the looking up of the date of the next full moon, the looking up of the first high tide for a given home port on the date of the next full moon, the marking of the cover plate with a home port date line and a moon line, and the rotation of the home port date line" to a given date on the first scale to determine from the index marks on the cover plate the times of the various tides on that date. The moon line will then point to the phase of the moon for the given date.

The foregoing and other objects, advantages, and features of the invention and the manner in which the same are accomplished will become more readily apparent upon consideration of the following detailed description when taken in conjunction with the accompanying drawings, which illustrate a preferred and exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of computation apparatus of the invention with a portion of the spiral scale shown in phantom line;

FIG. 2 is an enlarged partial view of the base board of the apparatus of FIG. 1; and

FIG. 3 is an exploded view of the computer apparatus of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning first to FIG. 1, it will be seen that the computation apparatus of the invention comprises a base board having a first scale 102 of spiral configuration surrounded by a circular second scale 104 which, in turn, is surrounded by a third circular scale 106. A transparent cover disc or plate 108 is mounted, as will be presently described, for rotation over base board 100. An arm 110 is mounted for rotation over cover disc 108 and has a straight edge 112 which will serve as a scribing guide as will be presently described. With reference to the exploded view of FIG. 3, it will be noted that a rivet 114, or the like, is provided to extend through holes 116 in arm 110, 118 in cover disc 108, and 120 in base board 100 and serves as an axis for rotation of cover disc 108 and arm 110 relative to base board 100.

Returning to FIGS. 1 and 2, it will be noted that spiral scale 102 includes a plurality of successive sections, each extending along a path corresponding to the whole length of the second scale 104. Scale 102 is formed of a plurality of indicia such as indicia 122 designating the names of months and, associated with index marks 124, the days of the month. It will be understood that 12.36 revolutions of spiral scale 102 are provided. This number of revolutions is obtained by dividing the number of days of a normal year, namely 365, by the number of days in the lunar month, namely 29.5305884, one revolution of cover disc 108 thus representing 1 lunar month. It will be noted that the days of the year are spaced at equal angles around the spiral which is concentric with the axis provided by rivet 114. In order to determine the magnitude of the angle, the number of degrees in a circle, namely 360 degrees, is divided by 365 days. Thus, 12.1907 degrees are provided as the angular interval between index marks 124 designating each of the days of the normal year.

Although it would be possible to start the date spiral at Jan. 1 (at its outermost point) and end it at the innermost point at Dec. 31, this arrangement would provide problems in leap years such as 1972. This would be because an additional day, Feb. 29, would need to be inserted at an intermediate point of the spiral. This would require that the setting of the device, which will be described hereinafter, would have to be repeated immediately subsequent to Feb. 29. On the other hand, by providing Mar. 1 as the beginning point of the scale, as is readily seen in FIG. 2, and by ending the scale at Feb. 29 (see FIG. 1) at the innermost point thereof, it is possible to set the device just once each year. As already mentioned, an extra date space is provided at the innermost point of the spiral for Feb. 29. This will be added to the 12.36 revolutions provided for a normal 365 day year. Thus the apparatus is reset on the last day of Feb. regardless of whether it is a leap year or not.

The second scale 104 on base board 100 designates the hours of the day. Numerals 126 designating the hours are associated with corresponding index marks 128, one such index mark being provided for each hour. The third scale 106 shows the various phases of the moon and includes a full moon 130 at a point corresponding to midnight, a three-quarter moon 132 at 3:00 oclock, a half moon 134 at 6:00 oclock, a quarter moon 136 at 9:00 oclock, a new moon 138 at midday, a quarter moon 140 at :00 o'clock, a half moon 142 at 18:00 oclock, and a three-quarter moon 144 at 21:00 o'clock.

It is to be noted that cover disc 108 is transparent and is provided with a roughened upper surface to facilitate marking the surface with a pencil. A circular array of indicia designating the various stages of the tide is imprinted on disc 108. Thus, an index mark 148 is provided near the designation high" to signify the time of high tide, this index mark having an arrow head to distinguish it from the other index marks on disc 108. A second index mark 150 is provided near the designation now to designate the next low tide; a third index mark 152 is provided near the designation high to designate the next high tide; and a fourth index mark 154 is provided near the word low to designate the next low tide. A fifth index mark 156 is provided near the first high designation, being spaced from the first index mark 148 by a distance d. This distance d accounts for the approximately 50 minute variation in the time of a corresponding tide from day to day. In order to account for this variation, index marks 150, 152, 154, and 156 have been shifted in the following manner. Index mark 150 is positioned a distance from the first index mark 148 which is equal to 6 hours plus d/4. Index mark 152 is spaced from index mark 148 a distance which corresponds to 12 hours plus (2d)/4. Index mark 154 is spaced from index mark 148 in the clockwise direction along scale 104 a distance equal to eighteen hours plus (3d)/4. In like manner, as already explained, index mark 156 is positioned in a clockwise direction from index mark 148 by a distance equal to (4d)/4 or the distance d. In this way a vernier action is provided so that the time designations of the tide accurately reflect the shifting time of the tide from day to day. It will be noted that the designations ebbing and flooding" are provided between the designations high" and low and between low and high, respectively, to designate the intermediate stages of the tide when it is'changing from high to low and back to high again.

The use of the tide computation apparatus of the present invention will now be described. It is first necessary to look up the moons phases in an astonomical daily calendar. Such a calendar may be found in a standard world almanac or a prominent newspaper such as The New York Times. The calender is consulted to find the date of the next full moon. The next step is to consult a tide table to find the time of the high tide soonest after midnight for a home port for the date found as the date of the next full moon. Such tide tables are found in leading newspapers, or a standard reference such as Tide Tables, High and Low Water Predictions, 1972 East Coast of North and South America Including Greenland, issued in 1971, which is published by the United States Department of Commerce, National Oceanic and Atmospheric Administration and includes the times of tides at various prominent ports for every day in 1972. This reference work also provides tidal difference constants for various subsidiary points with reference to major ports. As will be described hereinafter, adjustments may be made for subsidiary points by using this information.

Recapitulating, if we take the date of the next full moon as Apr. 28, 1972 as shown in The New York Times for Tuesday, Apr. 11, 1 1972. and if we consider Baltimore, Maryland as the home port, the aforementioned tide tables will give 6:48 AM. as the first high tide at Baltimore, Maryland for Apr. 28, 1972.

The next step of the method is to set the cover disc 108 so that the high index mark 148 points to this time. Then, without moving the disc, arm is rotated to bring straight edge 112 over the index mark for the date of the next full moon or, in this example, to the index mark for Apr. 28. This is the position of the arm as shown in FIG. 1. A pencil is used to draw a line along straight edge 112. This line, which will be labeled home port date line, is shown at 158 in FIG. 1 in coincidence with edge 112 of arm 110. Without moving cover disc 108, arm 110 is then rotated to midnight on the second scale, and a moon line 160 is drawn by pencil in the same way. i

The cover disc 108 is now ready for use in computing the time of high and low tides at the home port on any day of the year by placing home port date line 158 over the appropriate date. Index marks 148, 150, 152, 154, and 156 will then point to high, low, high, low and high tides to be expected in sequence beginning on that date. It will be observed that moon line 160 will then simulataneously point to the phase of the moon on that date.

Any chosen port with different tide times may be entered in a similar manner with special home port date lines for each port computed in the manner described above. One such additonal home port date line is shown at 162. Where tide times are listed in the tide tables in termspf tidal differences, arm 110 is simply rotated counter-clockwise for plus and clockwsie for minus tidal differences for the listed number of hours and minutes for the ruling in of additional port lines for subsidiary ports. It is to be borne in mind, that the reading of tide times at any port is accomplished by setting that ports date line over the date in question. To find the phases of the moon, the disc is rotated to set the home port date line over the date in question. As already explained, the moon line will then point to the proper phase of the moon for that date.

It will be necessary to reset the tide computation apparatus of the present invention every year after Feb. 28 or Feb. 29 in a leap year. All pencil lines are erased and the procedure described hereinabove is repeated for the new year.

It will be understood that variations in the apparatus may include, for example, the provision of a straight rather than a circular rule. In this event, the successive portions of the date scale will be provided in parallel lines so that each successive section corresponds to a scale corresponding to the hours of the day. In such an embodiment, the marking arm 110 will move rectilinearly along the scales. Also, a helical rule is contemplated.

While a preferred embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

The invention claimed is:

l. Computation apparatus for determining the date and/or time of a recurrent periodic event, comprising:

a base board provided with a first scale having a plurality of index marks signifying the days of the year and a second scale having a plurality of index marks signifying the hours of the day, said first scale having a plurality of successive sections each extending along said second scale;

a transparent cover plate overlying said base board and said first scale, said cover plate having indicia thereon signifying the stages of said event; and

an arm mounted for movement over said cover plate and having a straight edge for facilitating the drawing of lines on said cover plate.

2. Computation apparatus as recited in claim 1, wherein said first scale is spiral and said sections are successive convolutions of said spiral and wherein said second scale is circular and surrounds said first scale.

3. Computation apparatus as recited in claim 2, wherein said event is the tide and said first scale has a number of said convolutions N governed by the equation:

where L is the number of days in a lunar month, being equal to 29.5305884.

4. Computation apparatus as recited in claim 3, wherein N 12.36 and wherein the angle between said index marks of said first scale is 12.1907 degrees.

5. Computation apparatus as recited in claim 3, wherein the outermost index mark on said first scale the date Mar. 1 and the innermost index mark on said first scale signifies the date Feb. 29.

6. Computation apparatus as recited in claim 2, wherein said cover plate is rotatable on said base board about an axis concentric with said spiral first scale and said arm is rotatable about said axis to place said straight edge along radial lines with respect to said axis.

7. Computation apparatus as recited in claim 6, wherein the upper surface of said cover plate is roughened to facilitate marking said cover plate with a pencil.

8. Computation apparatus as recited in claim 6, wherein said event is the tide and said indicia on said cover plate include a first indexmark signifying high tide, a second index mark signifying low tide, a third index mark signifying high tide, and a fourth index mark signifying low tide.

9. Computation apparatus as recited in claim 8, wherein said cover plate is further provided with a fifth index mark signifying high tide, said fifth index mark being spaced clockwise from said first index mark a distance d along said second scale corresponding to the approximate 50 minute difference in time between corresponding high tides on successive days, the second index mark being spaced clockwise from said first index mark by a distance equal to six hours plus (1/4, the third index mark being spaced clockwise from said first index mark by a distance equal to twelve hours plus (2d/4), and the fourth index mark being spaced clockwise from said first index mark by a distance equal to 18 hours plus (3d/4).

l0. Computation apparatus as recited in claim 9, further comprising a third circular scale signifying the phases of the moon with a full moon being positioned at midnight and a new moon being positioned at midday of said second scale.

11. A method of computing the time of tides for a particular port, comprising:

providing computation apparatus as recited in claim looking up the moons phases in an astronomical daily calendar for a selected date and determining the date of the next full moon;

looking up in a tide table the time of the high tide most closely following midnight for said particular port on said date of the next full moon;

rotating said cover plate of said apparatus to being said first index mark in coincidence with said time for the high tide most closely following midnight on said second scale; rotating said arm to being the straight edge of said arm in coincidence with the index mark for the date of the next full moon on the first scale;

marking the surface of said cover plate along said straight edge of said arm to form a home port date line;

rotating the arm to bring the straight edge of said arm in coincidence with the index mark for midnight on saidsecond scale;

marking the surface of said cover plate along said straight edge of said arm to form a moon line;

rotating said cover plate to bring said home port I date line in coincidence with the index mark for a given date on said first scale; and

determining from the times on said second scale coincident with said index marks on said cover plate the times ofthe tides for said given date corresponding to said index marks on said cover plate.

12. A method as recited in claim 1 1, further comprising the step of determining the phase of the moon on said given date by noting the moon phase on said third scale coincident with said moon line" when said home port date line is aligned with said given date on said first scale.

13. Computation apparatus as recited in claim" 2, wherein said event is the phase of the moon and said first scale has a number of said convolutions N governed by the equation:

where L is the number of days in a lunar month, being equal to 29.5 305884, and wherein said apparatus further comprises a third circular scale signifying the phases of the moon with a full moon being positioned at midnight and a new moon being positioned at midday of said second scale.

* F t t 

1. Computation apparatus for determining the date and/or time of a recurrent periodic event, comprising: a base board provided with a first scale having a plurality of index marks signifying the days of the year and a second scale having a plurality of index marks signifying the hours of the day, said first scale having a plurality of successive sections each extending along said second scale; a transparent cover plate overlying said base board and said first scale, said cover plate having indicia thereon signifying the stages of said event; and an arm mounted for movement over said cover plate and having a straight edge for facilitating the drawing of lines on said cover plate.
 2. Computation apparatus as recited in claim 1, wherein said first scale is spiral and said sections are successive convolutions of said spiral and wherein said second scale is circular and surrounds said first scale.
 3. Computation apparatus as recited in claim 2, wherein said event is the tide and said first scale has a number of said convolutions N governed by the equation: N (365/L) where L is the number of days in a lunar month, being equal to 29.5305884.
 4. Computation apparatus as recited in claim 3, wherein N 12.36 and wherein the angle between said index marks of said first scale is 12.1907 degrees.
 5. Computation apparatus as recited in claim 3, wherein the outermost index mark on said first scale signifies the date Mar. 1 and the innermost index mark on said first scale signifies the date Feb.
 29. 6. Computation apparatus as recited in claim 2, wherein said cover plate is rotatable on said base board about an axis concentric with said spiral first scale and said arm is rotatable about said axis to place said straight edge along radial lines with respect to said axis.
 7. Computation apparatus as recited in claim 6, wherein the upper surface of said cover plate is roughened to facilitate marking said cover plate with a pencil.
 8. Computation apparatus as recited in claim 6, wherein said event is the tide and said indicia on said cover plate include a first index mark signifying high tide, a second index mark signifying low tide, a third index mark signifying high tide, and a fourth index mark signifying low tide.
 9. Computation apparatus as recited in claim 8, wherein said cover plate is further provided with a fifth index mark signifying high tide, said fifth index mark being spaced clockwise from said first index mark a distance d along said second scale corresponding to the approximate 50 minute difference in time between corresponding high tides on successive days, the second index mark being spaced clockwise from said first index mark by a distance equal to six hours plus d/4, the third index mark being spaced clockwise from said first index mark by a distance equal to twelve hours plus (2d/4), and the fourth index mark being spaced clockwise from said first index mark by a distance equal to 18 hours plus (3d/4).
 10. Computation apparatus as recited in claim 9, further comprising a third circular scale signifying the phases of the moon with a full moon being positioned at midnight and a new moon being positioned at midday of said second scale.
 11. A method of computing the time of tides for a particular port, comprising: providing computation apparatus as recited in claim 10; looking up the moon''s phases in an astronomical daily calendar for a selected date and determining the date of the next full moon; looking up in a tide table the time of the high tide most closely following midnight for said particular port on said date of the next full moon; rotating said cover plate of said apparatus to being said first index mark in coincidence with said time for the high tide most closely following midnight on said second scale; rotating said arm to being the straight edge of said arm in coincidence with the index mark for the date of the next full moon on the first scale; marking the surface of said cover plate along said straight edge of said arm to form a ''''home port date line;'''' rotating the arm to bring the straight edge of said arm in coincidence with the index mark for midnight on said second scale; marking the surface of said cover plate along said straight edge of said arm to form a ''''moon line;'''' rotating said cover plate to bring said ''''home port date line'''' in coincidence with the index mark for a given date on said first scale; and determining from the times on said second scale coincident with said index marks on said cover plate the times of the tides for said given date corresponding to said index marks on said cover plate.
 12. A method as recited in claim 11, further comprising the step of determining the phase of the moon on said given date by noting the moon phase on said third scale coincident with said ''''moon line'''' when said ''''home port date line'''' is aligned with said given date on said first scale.
 13. Computation apparatus as recited in claim 2, wherein said event is the phase of the moon and said first scale has a number of said convolutions N governed by the equation: N (365/L) where L is the number of days in a lunar month, being equal to 29.5305884, and wherein said apparatus further comprises a third circular scale signifying the phases of the moon with a full moon being positioned at midnight and a new moon being positioned at midday of said second scale. 